The Origin of Species by Means of Natural Selection; Or, the Preservation of Favored Races in the Struggle for Life ...

according action adapted admit advantage allied America amount animals appear become believe belonging birds breeds called cause certain characters climate closely color common considered continued crossed descended developed difficulty distinct domestic doubt effects existing extinct extremely facts favorable fertility flowers follow formation forms genera genus give given groups habits hand Hence hybrids important increase individuals inhabitants inherited insects instance instincts intermediate islands kind known land laws less living look male manner means modified namely natural selection naturalists nearly observed occur organs origin parent perfect period plants points present principle probably produced range ranked reason remarked resemblance respect seeds seems seen separated shown side similar single slight sometimes species stage sterility structure successive suppose tend theory tion variability variations varieties various vary whole widely young